1. Field
Apparatuses consistent with the present invention relate to removing a leakage signal from a radio frequency identification (RFID) reader.
2. Description of the Related Art
Among systems using same transmission and receiving frequencies, radio frequency identification (RFID) systems are the most widely used. RFID systems are deployed with a wireless recognition system technology in which an electronic chip is attached to a desired object to be recognized through a wireless frequency, the object to be recognized is identified, and information stored in the electronic chip is obtained. Also, the RFID systems are a base for a next-generation ubiquitous sensor network (USN) for unifying information about an object to be recognized, by using the electronic chip in a network. An RFID system generally includes an electronic chip attached to an object to be recognized and containing information about the object, and a reader for collecting the information.
Most widely-used wireless communication systems use different bandwidths for receiving and transmission frequencies. However, in the case of a system using the same transmission and receiving frequencies like an RFID system, a transmission signal should be transmitted continuously from a reader side even in the instant that the reader is receiving a receiving signal so that an electronic chip can generate the receiving signal using power of the transmission signal.
The reader includes a digital processor (not shown) for processing the information about the object to be recognized, and a transmission and receiving unit (not shown) for signal transmission and receiving. In a general communication system, one antenna is used, and different frequencies are used when transmitting and receiving signals. Thus, for separation between signal transmission and signal receiving, an element that operates on different paths according to frequencies, such as a duplexer is used, thereby separating transmission and receiving signals from each other.
However, in a transmission and receiving system using a same frequency like in an RFID system, transmission and receiving signals are separated from each other by using an element for transmitting a signal only in one direction according to an input port. As an example thereof, a circulator or a directional coupler that is an element for separating transmission and receiving signals is used.
A feature of an RFID system is that a transmission signal should be transmitted while a receiving signal is being received. This kind of a transmission and receiving system is constituted using a circulator or a directional coupler having a good separation capability between ports so as to separate transmission and receiving signals from each other. However, since the circulator or the directional coupler does not have a characteristic of an idealistic element, an impedance mismatching phenomenon occurs between an output unit of the circulator or directional coupler and an antenna. Thus, the transmission signal is reflected. The reflected transmission signal is input to a receiving unit and is called a reflected transmission leakage signal. The reflected transmission leakage signal is input to the receiving unit and causes degradation of performance of the receiving unit. Also, since the reflected transmission leakage signal has a larger magnitude than that of the receiving signal including information received by an electronic chip, a capability for recognizing the electronic chip of the entire system may also be reduced.